The present invention relates to a rolling bearing having a bearing ring made of a ceramics.
In mounting a seal member to a (rolling) bearing ring made of a ceramics, for example, the seal member is fitted to an even shoulder portion of a peripheral face of the bearing ring on a side of a raceway, or fitted to a seal groove formed at the shoulder portion (refer to, for example, JP-A-11-247864). The seal groove in this case is constituted by a shape the same as that of a seal groove provided at a general bearing ring made of a metal, that is, an inside corner shape in which a diameter thereof is gradually increased from an end edge in an axial direction to the side of the raceway, a groove depth is deep and which is provided with a comparatively acute angle.
In the above-described example of the related art, the groove shape of the seal groove of the bearing ring made of a ceramics is constituted by the shape the same as the shape of the seal groove of the general bearing ring made of a metal and therefore, the shape amounts to an increase in cost such that time is taken in cutting or the like.
On the other hand, a ceramics is used for a member of a bearing used under a special environment of under a corrosive gas atmosphere or the like in consideration of durability (corrosion resistance) of a bearing material against the environment. A ceramic rolling bearing constituting inner and outer rings by a ceramics is frequently used by a constitution of an open type (without seal) since workability thereof is poorer than a general rolling bearing using bearing steel and it is difficult to form (process) a deep groove for mounting a seal (refer to, for example, JP-B-6-17688).
In a related art, in order to achieve long service life of such a ceramic rolling bearing, as means for hermetically sealing an opening thereof, there has been proposed a method of ensuring sealing performance by respectively mounting members substituting for seals on outer sides of both end portions of a fixed ring and covering openings of a ring-like space by the members (refer to, for example, JP-A-6-337016).
Meanwhile, when a sealing plate (shield) made of a metal is used for a rolling bearing in which inner and outer rings thereof are made of a ceramics, strict dimensional accuracy is required for the sealing plate and sealing plate mounting grooves (mounting faces) of the inner and outer rings made of a ceramics which are difficult to work and therefore, there poses a problem that working cost is increased. Further, in an environment requiring corrosion resistance, there is a case in which the metal-made sealing plate per se is corroded and cannot be used.
Further, when the seal mounting grooves are provided at end faces of the inner and outer rings made of a ceramics which is a brittle material, there is produced an inside corner (inside angular portion) accompanied by an abrupt change in an angle at a portion of the groove shape and there also is a concern of initiating a crack or the like by constituting an onset by the inside corner.